The invention relates to a leaf spring system, in particular for influencing at least one body operating or comprising one or more contacts of an electric switch, with a chassis and at least one leaf spring which can act on the at least one body. The invention also relates to leaf spring combinations to be used with and to electric switches provided with such a leaf spring system.
A leaf spring system of this type is for instance known from German Patent Specification DE-C-3,326,220.
In electric switches various switching functions are fully or partially dependent on a spring system. For example, spring systems are used, inter alia, for obtaining the force with which contacts are held against each other (contact force), in order to meet certain conditions under which the contacts have to open or close (threshold values), for achieving a desired switching speed etc. The choice of the spring system greatly affects both the working of the switch and the design thereof.
In most known spring systems helical tension or compression springs are used. These springs act with one end on the body to be influenced, for example a contact arm, while the other end is attached to the housing or the chassis of the switch. The forces exerted by these springs also act on the attachment of the spring to the housing or the chassis. In particular when relatively great forces have to be exerted, this attachment, and therewith the housing or the chassis, will have to be sturdy enough to absorb such great forces.
Moreover, a spring for achieving a particular function, for example for producing the contact force, often works badly, i.e. counterproductively, for producing another switching function such as, for example, the contact opening speed. In order to keep the effect of this poor working to a minimum, an additional requirement which is often set is that the working of the spring system must be degressive. This means that the influence of, for example, the contact force spring when another switch function comes into operation, for example the opening of the contacts, must decrease very rapidly and in some cases must even reverse its direction of operation. In order to make it possible to comply with such a requirement, the action point of the spring on the body to be influenced, the attachment point of the spring to the housing or the chassis and the rotation or hinge point of the body to be influenced are geared to each other in the overall construction in such a way that a decreasing couple or even one reversing in direction is produced. However, such a solution requires a relatively complex construction of springs and levers, such as for example that disclosed in European Patent Application EP-A-127,784.
A complex spring system is also necessary if a linear movement of, for example, a contact arm has to be carried out instead of a rotary movement. In order to obtain a degressive action, use will also have to be made here of lever systems and the like. With such complex constructions it is also so that if, in order to obtain as compact a construction as possible, one wishes to reduce the size of the moment arm of the body to be influenced by the spring action, the force to be produced by the spring will have to increase while the couple remains the same. The consequence of this again is that the spring itself will have to be stronger and thus larger, so that part of the envisaged space saving effect is wiped out. Furthermore, the action point and thus also the housing or the chassis will have to be designed for this greater force.
The leaf spring system disclosed in the above mentioned German Patent Specification 3,326,220 also has the disadvantage that the tension exerted on the housing or the chassis of the electric switch by the leaf spring acts on and causes wear in the hinge points of the leaf spring or of the body influenced by the leaf spring which are situated in the housing or the chassis. Since the housing or the chassis is generally made of plastic, these hinge points therefore require great attention and, particularly in the case of relatively great forces to be exerted by the leaf spring, must be of a special design and/or material composition.
The French Patent Specification 2,057,181 discloses also a leaf spring system for influencing the contact mechanism of an electric switch. The leaf spring can be brought in tensed position by means of a control knob and a connecting rod, said connecting rod being forced along a guide member. In tensed position, the leaf spring exerts a force on the contact mechanism as well as on the control knob, in particular their attachment or hinge points to the housing or chassis of the switch.
Of course, the housing or the chassis must be sufficiently sturdy to withstand the forces exerted on them by the leaf spring. For the abovementioned reasons, leaf spring systems of this type are seldom used in electric switches and only then if relatively small forces have to be exerted.
The object of the invention is therefore to produce a leaf spring system by means of which the abovementioned disadvantages of the known spring systems are eliminated, and in which the leaf spring system can also be simple and compact in design and can easily be adapted to the spring action required for a particular application, and comprises or needs a minimum of parts or aids.
This is achieved according to the invention in that the leaf spring system comprises a supporting frame for receiving in the frame aperture thereof, supported at one end, the at least one leaf spring, while in the frame aperture between the projecting free end of the leaf spring and the edge of the supporting framesituated opposite that end--the at least one body to be influenced by the spring action can be accommodated the dimensions of said body in the frame aperture being greater than the distance between the said edge of the supporting frame and the free end of the at least one leaf spring when the latter is situated essentially in the plane of the supporting frame, said supported frame being rigidly supported by the chassis.
In this context, with the term "rigidly supported" it is meant that said supporting frame is beared on the chassis, such that the supporting points for the at least one body to be influenced by the spring action and the at least one leaf spring of said supporting frame have a relative fixed position. For instance, this can be achieved by bearing the supporting frame on all sides or by using a suitable designed chassis for at least fixing the said supporting points. A supporting frame which is sufficiently rigid may be for instance mounted at the end sides thereof.
The leaf spring system according to the invention constitutes for virtually the most part a socalled closed force system, which means that the tension exerted by the leaf spring is largely absorbed by the combination of the leaf spring, the body and the supporting frame. This means that much lower strength requirements are needed for the housing or the chassis in which the leaf spring system according to the invention is mounted, compared to the known leaf spring systems, which results in a lower wall thickness and also a lower production accuracy, since no further requirements need be laid down for positioning and design of attachment points.
Even in switches in which relatively great forces have to be exerted by the leaf spring, the leaf spring system according to the invention can be mounted directly in a housing of, for example, plastic. The leaf spring system according to the invention is both simple in design and compact in construction, so that the dimensions of the switch in which such a leaf spring system is used can be smaller than corresponding switches with a spring construction provided with lever systems, coil springs and the like.
It is pointed out that U.S. Pat. No. 2,685,007 discloses a leaf spring system for use in an electric switch, comprising a frame, in the frame aperture of which a leaf spring and a body to be influenced by the leaf spring is accommodated. However, the frame actively takes part in the spring action of the leaf spring system. Such, in that the frame is movably positioned for acting as a bending spring, in order to achieve the specified switching function.
In contrast to the supporting frame according to the invention, the frame in this known leaf spring system is not rigidly supported by a chassis, such that only a force action transverse to the frame aperture can be effectively used, i.e. in the direction of movement of the frame. Because of the rigid support of the supporting frame according to the invention, the tension in longitudinal direction of the leaf spring can be used, for instance to achieve a specified contact force or switching speed. The tension in longitudinal direction of a leaf spring can be a multiple of the said force in transverse direction.
British Patent Specification 538,317 discloses also a leaf spring system with a frame, in the frame aperture of which a body is accommodated on which two leaf springs are acting. However, the frame is also movably supported to achieve the desired spring action. This embodiment differs further from the leaf spring system according to the invention, in that the body is not supported by an edge of the frame, but by the free ends of the opposite leaf springs. Even by rigidly supporting said frame according to the invention, it is not possible to use the bending force of the leaf springs, because putting one leaf spring under tension results in a deflection of the other leaf spring, as a consequence of which the position of the supporting point of the body of said other leaf spring is moved.
Further it is pointed out that German Patent Application DE-A-3409393 also discloses a spring system and an electric switch in which the force exerted by the spring is not transferred directly to the housing or the chassis of the switch either. However, this is not a leaf spring system, nor is it a leaf spring system which is integral with a supporting frame such as that in the invention. Besides, the force exerted by the spring does not lie in the plane of a frame as in the case of the invention. Deformation of the supporting frame is therefore quite possible here.
The supporting of the leaf spring by the supporting frame is achieved in an embodiment of the spring system according to the invention in such a way that the at least one leaf spring at the supported end thereof is integral with the supporting frame and extends from this end into the frame aperture.
Depending on the required spring force, the length of the leaf spring and its deflection relative to the frame aperture, such great bending stresses can occur on the transition between the leaf spring and the supporting frame that cracks occur or the spring material is stressed even to above its yield point, which in the end leads to rupture. Particularly in compact, relatively small switches with high contact force and/or switching speed, it is advantageous to use the leaf spring system according to a further embodiment of the invention, which is characterized in that the at least one leaf spring is detachably supported in the frame aperture.
According to yet another embodiment of the invention, this method of supporting is achieved in such a way that a supporting element for detachably supporting the at least one leaf spring is disposed in the frame aperture between the end of the at least one leaf spring to be supported and a further edge--situated opposite that end--of the supporting frame. The bending force acting in the supporting point on the leaf spring is now transferred to the supporting frame via the hingedly supported end thereof and the supporting element, so that the bending stresses occurring in the supporting point are greatly reduced compared with the embodiment in which the leaf spring is integral with the supporting frame. According to the invention, the supporting element can be a further body of an electric switch to be influenced by the spring action.
With the leaf spring system according to the invention it is fairly simple to obtain the required degressive action. For this, it is only necessary to make a suitable selection relative to each other of the points of action of the end of the leaf spring and the opposite edge of the supporting frame on the body to be influenced by the spring action. With a proper selection of the points of action and the shape of the body, it is possible to produce either a rotary or a linear movement thereof, so that the leaf spring system according to the invention can be used in various types of electric switches. The size and direction of the force exerted by the leaf spring on the body can also thus be determined.
An embodiment of the leaf spring system according to the invention provided with at least one body to be influenced by the at least one leaf spring, with which such degressive action is obtained that the spring action changes direction, is characterized in that the at least one body comprises an arm which projects from the frame aperture and can make a rotary movement about the opposite edge of the supporting frame, said arm being capable of producing such bending of the at least one leaf spring that when the arm is moved against the spring action past a transition point, the spring action thereon reverses direction and the at least one leaf spring can exert a force on the arm in this reversed direction of movement.
An embodiment of the leaf spring system according to the invention which is advantageous for practical applications in an electric switch is characterized in that the leaf spring system comprises two leaf springs which extend in line with each other from a common frame part for supporting the leaf springs, in such a way that the free ends of said leaf springs each point in an opposite direction, each free end of the respective leaf springs being able to act on an appropriate arm.
Such a construction with two arms can also be achieved advantageously in that the further body comprises a similar arm, the distance between the two bodies in the frame aperture being smaller than the length of the at least one leaf spring when the latter is situated essentially in the plane of the supporting frame. The leaf spring here is thus hingedly clamped in the frame aperture between the two arms. The two arms can project in the same direction or in opposite directions from the plane of the frame aperture.
Instead of rotary arms, movable contact blocks can, for example, also be incorporated in the frame aperture as a body. According to yet another embodiment of the leaf spring system according to the invention, this is achieved through the fact that the at least one body is hingedly connected to the free end of the at least one leaf spring and is movable in a direction at right angles to the opposite edge of the supporting frame.
Such a spring system can also be further constructed according to the invention in such a way that the at least one body under the influence of the at least one leaf spring can assume a first position in which the body is removed from the opposite edge of the supporting frame and a second position in which the body rests under spring force against the opposite edge of the supporting frame.
In order to reduce the mechanical stresses working in the supporting point of the leaf spring and/or in order to obtain an envisaged spring action, the leaf spring can be shaped as required, deviating from its rectangular basic shape. For a reduction of the mechanical stresses in the supporting point, the leaf spring can be widened out towards its end which is to be supported, being for example trapezoidal. The free end of the leaf spring acting on the body can be made in widened form in order to bring about good distribution of the forces in the action point with the body. The at least one leaf spring can to this end also consist of several spring strips connected to each other at one end.
A compact construction of an electric switch with a leaf spring system according to the invention, in addition to a minimum of parts, is also achieved in that the leaf spring may be loaded to its breaking limit, so that with this leaf spring great forces can be exerted, thereby making it possible to select a small moment arm, so that the construction of the switch can be compact in certain respects. Through the largely closed force construction of the spring system, the housing or the chassis by which the supporting frame is supported can still be kept light in construction.
The leaf spring and the supporting frame can be made of a strip of spring material by punching, stamping, spark erosion or etching.